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D. DRAWBAUG-H. TELEPHONE TRANSMITTER.

No. 540,781. Patented June 11,1895.

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' D. DRAWVBAUGH.

TELEPHONE TRANSMITTER. N0. 54.0,781. Patented June 11, 1895.

Law an /07" U ITED STATE-S PATENT QFFI E DANIEL DRAWBAUGH, OFEBERLYS MILL, PENNSYLVANIA, ASSIGNOR TO THE DRAWBAUGHTELEPHONE AND TELEGRAPH COMPANY, OF NEW YORK, N. Y;

TELEPHONE-TRANSMITTER.

SPECIFICATION forming part of Letters Patent N... 540,781, dated June 11, 1895. 1

Application filed February 16, 1895. Serial no. 538,694. (No model.)

To all whom it may concern;

Be it known that I, DA NiEL DRAWBAUGH, of Eberlys Mill, in the county of Cumberland, State of Pennsylvania, have invented certain new and useful Improvements infTelephone- Transmitters; and I do hereby declare the following to be a full, clear, and exact description of the same, reference being had totheaccompanying drawings, forming-apart of this specification, and to the letters of reference marked thereon.

This invention relates toimprovements in telephonic transmitters and particularly to that type in which comminuted material of low conductivity is employed as the resistance varying medium, the objects of the invention being, primarily, to provide a highly et'ficient instrument capable of universal use either as a long distance or local exchange instrument. j

A further object is to produce an instrument of exceedingly simple design whereby the manufacture is facilitated and. whereby the device is prevented from getting out of adjustment either through non use, rough handling or the ordinary wear and tear of use.

Referring to the accompanying drawings, Figure 1 is a front elevation of a transmitter embodying my present invention. Fig. 2 is a bottom plan view of the shelf on which it is mounted. Fig. 3 is a vertical section through the support, looking toward the front. Fig. 4: is a vertical section from front to rear through the operative parts and mouthpiece of the transmitter. Fig. 5 is a view with the back plate removed. Fig. 6 is a section through a modified form of diaphragm.

Like letters of reference in the several figures denote the same parts. p

I have shown in connection with my present transmitting instrument proper, by which I mean the resistance varying mechanism with its surrounding parts, a support consisting of a back board A provided with a shelf B carrying the induction coil 0 and binding posts 0' for the receiver. The back board also preferably carries the switch lever D of a well known pattern and the binding posts for the battery and line connections lettered E and F respectively. The receiver and secor the receiver is connected in a shunt around the secondary of the induction coil. The battery circuit runs from one of the posts E to the switch, thence to the primary of the coil and .to the metallic portion of the hollow standard G fastened on the shelf. The other battery connection passes from the other post E by an insulated conductor up through the hollow standard and is connected at the top to an insulated contact g all as shown in Figs. 1 and 3.

ondary of the coil are connected in multiple The shape of the standard G or the employment of anystandardat all is optional, as is also the particular wiring'or circuit connections describedinsofar as the operative parts which will now be described are concerned, and, therefore, I do not wish to be limited to the particular details heretofore set forth.

The body of the transmitter proper may be of ny desired shape or material but in the form illustrated it'is composed of a hard insulating substance for convenience made in the form' of an annulus H, that is to say, it has arelatively large opening'h, while at the front it isslightly recessed'for the reception of the diaphragm I. The latter is held in place by the cover piece K screwed down upon it so as to clamp its edge against the body H. This cover has the usual mouth piece it and is itself together with the mouthpiece preferably struck or spun up from sheet metal the two parts being screwed together, as shown. At the center, the diaphragm I, in the instrument shown, carries one of the electrodes to be presently particularly described, and surrounding the electrode and resting against the diaphragm is a disk L of felt or similar material, preferably felt and of such external diameter as to fit into the opening in the body. The rear side of the body is provided with a plate M clamped in place by screws or otherwise'and the felt or fibrous material is held forward against the diaphragm with a moderate pressure so as to dampen the latter against false vibration without interfering with the true or direct vibrations due to the impact of sound waves. The back plate M in the form shown carries the rear electrode and the circuit is established on the one hand through a bearing piece m on the back plate which co-operates with a similar plate m on the standard, the two being held in adjusted position by a set screw m and on the other hand, through a contact finger m secured to the body H in electrical connection with the diaphragm, and adapted to bear on the contact piece g. The receptacle for the comminuted resistance conductor, preferably granular carbon indicated by the letter N, is directly in the fibrous or felt pad through which an opening of just proper size for the entry of the electrodes is formed and the electrodes themselves, lettered respectively 0 and 0 close each side of the opening forming a small chamber the walls of which by reason of their elastic nature effectually prevent any caking or packing of the comminuted resistance cond uctor. In the preferred construction the faces of the electrodes are of polished resistance conductor such as carbon. The carbon face of the front electrode is held by a central rearwardly extending offset t' and the carbon face of the rear electrode is held by a screw P screwing through the plate M. Obviously the faces of the ofi-set on the diaphragm and the face of the screw may be employed without the carbon and where cheapness is desired such construction will be found efficient. In Fig. 6 I have shown a diaphragm with the off-set simply struck out from its center by which construction the diaphragm and its electrode may be formed at a single operation.

While any ordinary diaphragm may be employed, I prefer to employ a diaphragm having a thickened edge as at Q whereby the diaphragm is retained under proper tension and buckling not only prevented but by simply striking and expanding the thick edge the strains may be equalized in the diaphragm and the diaphragm put under tension so as to secure the best results.

In setting up the instrument the parts are assembled with the exception of the rear screw. Then the comminuted material is poured in and the screw inserted. The distance between the faces of the two electrodes should be regulated according to the size of the particles of comminuted resistance conductor. Thus where fine material is used there should be a space of from one sixteenth to one eighth of an inch and the comminuted material should not quite fill the chamber when the instrument is standing in. vertical position. The best adjustment of the parts, however, is best determined by experimenting and thus while I have been specific in my description it will be understood that the proportions and relative arrangement of the supporting parts are susceptible of wide variations without departing from the spirit of my invention.

The annular form of the pad of felt or similar material whereby the electrodes may be located at the center of the diaphragm gives a most perfect dampening effect without injuring the efficiency of the instrument and this effect would be secured even though the pad did not form the chamber for the comminuted resistance varying conductor.

I do not make claim herein to the employment of comminuted or subdivided resistance varying conducting material, this feature of the invention, together with the general cooperative arrangement of electrodes and re sistance varying medium being described and claimed in my prior application, Serial No. 111,554, filed November 12, 1883.

Having thus described my invention, what I claim as new is- 1. In a telephonic transmitter, the combination with the electrodes movable toward and from each other, of abody of feltor similar material having an opening into which said electrodes fit and work, and a comminuted resistance conductor confined thereby between the proximate faces of the electrodes; one of said electrodes being attached to adiaphragm which latter bears against the face of the body of felt or similar material substantially as described.

2. In a telephonic transmitter, the combination with the electrodes movable toward and from each other, and the diaphragm connected with one of said electrodes, of a felt pad bearing against the diaphragm and having a central opening into which the electrodes fit and work and a comminuted resistance conductor confined between the proximate faces of the electrodes by the felt pad; substantially as described.

3. In a telephonic transmitter, the combination with the body having the central openin g, the diaphragm and rear plate, of the electrodes, a felt pad held in the central opening in the body and surrounding the electrodes to form a chamber between them and comminuted resistance conductor located in the chamber; substantially as described.

4. In a telephonic transmitter, the combination with the diaphragm and electrodes, of the fiat elastic pad having an aperture into opposite sides of which the electrodes fit, thereby surrounding the electrodes to form a chamber between them and bearing against the diaphragm and the plate 011 the rear side of the pad for holding it in contact with the diaphragm; substantially as described.

5. In a telephonic transmitter, the combination with the body having the central opening, the diaphragm and rear plate, of the electrodes, an annular pad of felt or similar material fitting in the central opening surrounding the electrodes to form a chamber between them and filling the space between the diaphragm and rear plate, whereby the diaphragm is dampened and comminuted resistance conductor located in the chamber; substantially as described.

6. A diaphragm for telephonic transmitters having a rearwardly extending central offset consti-tutin g an electrode; substantially as described.

7. In a telephonic transmitter, the combination with a diaphragm having a central rearwardly extending off-set constituting an electrode, of a pad of felt or similar material surrounding said electrode, a second electrode projecting into the said pad from the rear and comminuted resistance conductor located between the electrodes; substantially as defelt pad fitting in the opening in the body and having the central opening for the electrodes, the rear plate supporting the pad against the diaphragm and the adjustable electrode passing into the pad; substantially as described.

10. In a telephonic transmitter, the combination with the body, the diaphragm electrodes and dampening pad surrounding the electrodes, of the rear plate for supporting the rear electrode, the rearwardly extending lug on said plate and a metallic support with which said lug is adj ustably connected; substantially as described.

11. A diaphragm for telephones having a malleable thickened edge whereby the diaphragm may be strained by expanding the edge; substantially as described.

DANIEL DRAWBAUGH. Witnesses:

MARCUS MARX, WILLIAM M. HAIN. 

